820-00164 SMC_RESET_L issue.

[JohnB8812]

Ok so this one has me confused unless the SMC is causing this. Board came in badly liquid damaged replaced many components too this point. Original corrosion definitely around SMC reset IC and SMC as well as many other things. Board has now been ultrasoniced to rule out flux under SMC. PPBUS is 8.18 volts with a U5110 on the board and SMC Reset goes low. When I take it off, PPBUS goes back to 8.58, I get a light on the charger, and I get a quarter spin for the IC missing. So I thought ok bad IC from donor board. I have now tried 5 different ICs and I get the same issue 8.18 with the chip on and 8.58 with chip off. Is the SMC pulling it low with the IC on or do I seriously just have tons of bad SMC reset ICs from donors? Or could this be an internal board issue? I'm completely confused at this point for sure known good DC in board and flat cable and pullup for SMC_RESET_L measures 100K like it should. Any ideas?

 

[dukefawks]

Checked more voltages on pins of U5110? If it doesn't receive power it will pull down Reset of course.

 

[JohnB8812]

Pins 3 and 6 measure 3 volts. Pin 8 measures .89 volts. I would assume that means an issue with the SMC?

 

[dukefawks]

Why did you not measure pin 1 and 4? Pin 8 should of course have 3V on it. Check if it has low resistance to GND.

 

[JohnB8812]

Pin one 3.42 volts, pin 4 zero volts as well. Many kilohms to ground on pin 8

 

[dukefawks]

pin 4 should not be 0V, resistance to GND there.

 

[JohnB8812]

8 million ohms. Also the first time I plugged this in this morning, I somehow got a green light. I then unplugged and plugged back in and got no light.

 

[JohnB8812]

Also no short on any of the pins of U5110 all measure ok.

 

[dukefawks]

This must be a U5110 issue or one of its traces. Pin 4 should always come up to about 2.75V.

One way to bypass U5110 is to take it off the board. Then power up the board and manually short SMC_RESET to GND. This will give the SMC a known good start. PPBUS should then come up at 8.6V and board should start. Once that works we can worry about U5110 further.

 

[JohnB8812]

Ok with U5110 off the board and doing what you said it did SMC Reset. PPBUS goes to 8.6 volts, but the board does not turn on. I get cycling on PP5v_S4RS3 and I also get cycling to about 300 millivolts on CPU VCore.

 

[JohnB8812]

PPVRTC_G3H is steady. The S4 rails are the rails cycling the S5's are steady. S4 on down to VCore is pulsing. I also want to say this board does not have an LP8550 on the board at the moment as I have them on order. Can that cause this issue? I figured not..

 

[JohnB8812]

Also noticed with no U5110, the SMC_RESET_L signal comes high to 3.4, but pin 8 is 150 millivolts and pin 4 is straight zero still.

 

[dukefawks]

Board works without LP8550.

SMC is missing AVREF now, just to be sure that is not causing issue connect pin 1 and 8 together where U5110 was and try again.

 

[JohnB8812]

Just tried still no power obvi getting 3.42 volts to 3v3 AVREF now tho. Still cycling tho. Bad SMC? There was corrosion everywhere on this btw but worst was definitely by SMC and U5110.

 

[dukefawks]

CPU Vcore cycling too? The usual suspects apply, U1950, U6100 and traces/resistors, J6100 and anything else really. Could be crap under SMC still too.

 

[JohnB8812]

VCore pulses to 300 milivolts. J6100 was removed first thing U1950 was replaced pin 8 getting 3.42. U6100 area amazingly was clean. I’m going to try a different SMC even tho it’s gonna suck. I think that could be the issue on this one

 

[JohnB8812]

Ok so back to this nightmare. I have replace the SMC. Without a reset IC on the board, 8.58 volts on PPBUS, 3.34 volts on SMC_RESET_L. HOWEVER, when I put my probe and measure SMC_RESET_L, the board SMC resets!!!! With an SMC_RESET_L IC on, it automatically pulls SMC_RESET_L to 0 volts. WHAT IS THE DEAL???? I'm so confused lmao

 

[JohnB8812]

Ok so there was definitely a broken trace between pin 3 and R5127. Jumped it, but now I get only a green light and the SMC reset signal is still 0 with a chip on the board but 3.3 without a chip. SMC_ONOFF_L is 3.4 volts. Pins 4 6 and 8 are being pulled down/cycling.

 

[JohnB8812]

In diode mode: 0.562 on pin 4, 0.567 on pin 6, 0.527 on pin 8 with the chip on the board. Millions of ohms to ground on pins 8 and 4 and 127 kohms on pin 6.

 

[JohnB8812]

Also with no ISL on the board, I get no green light at all. But I get 3v42.